Air-based respiration limits the use of aquatic environments by ancestrally terrestrial animals. To overcome this challenge, diving arthropods have evolved to respire without resurfacing using air held between their cuticle and surrounding water.1, 2, 3, 4 Inspired by natural history observations in Haiti (unpublished data) and Costa Rica,5,6 we conducted experiments documenting routine air-based underwater respiration in several distantly related semi-aquatic Anolis lizard species. Semi-aquatic anoles live along neotropical streams and frequently dive for refuge or food,7, 8, 9, 10, 11, 12 remaining underwater for up to 18 min. While submerged, these lizards iteratively expire and re-inspire narial air bubbles—underwater “rebreathing.” Rebreathed air is used in respiration, as the partial pressure of oxygen in the bubbles decreases with experimental submersion time in living anoles, but not in mechanical controls …